The kinescope or picture tube for color television has a triple gun, and requires color convergence coils disposed behind the main deflection yoke. One problem is a variation in the diameter of the glass neck of the tube. A typical tube specification may be plus or minus 1/16 inch for the neck diameter. Another problem is to secure best axial location of the convergence coil assembly on the neck of the tube. A further problem is to provide easily accessible means for adjustment of the electromagnets, as by means of a permanent magnet which is adjustable relative to the electromagnets.